i was worred too for about a week. I didn't sleep just watching her, but because she's been on her tummy her neck is so strong! She can move it side to side just fine. She sleeps so much better and after going through hell with DD1 sleep training (over a year) I have to get sleep. The only thing is that if I put her down right away she tends to spit up a little, I guess the pressure on her belly. I think that once she gets just a little older that won't be an issue. I asked my doctor about it, and he said its fine. I did ALOT of research on SIDS before I was comfortable with it and I've found that babies even die from SIDS on their back, and they THINK bellies are more dangerous. There are no nlankets or stuff animals etc and she's just fine. I have a friend who just lost her baby boy at 4 months from "SIDS" and was asleep in his back, so there you go.